Polyesters are polymeric materials made from the esterification of polybasic organic acids with polyhydric acids. Perhaps the most commonly made and used polyester is polyethylene terephthalate (PET), which can be manufactured by reacting terephthalic acid with ethylene glycol.
Polyesters are currently being used in increasing amounts in various applications. For instance, polyesters are commonly used to make many types of beverage and food containers, photographic films, X-ray films, magnetic recording tapes, electrical insulation, surgical aids such as synthetic arteries, fabrics and other textile products.
Because polyesters can be remelted and reformed, ongoing efforts are underway to efficiently recycle as much polyester as possible after use. Before polyester can be recycled, however, it is necessary to separate the post-consumer polyester from contaminants, i.e., materials that may be found mixed with or attached to the polyester. Many recycle processes include a separation step wherein the polyester is washed with an aqueous solution in order to separate the polyester from contaminants. While aqueous washing can remove many contaminants, it does utilize a great deal of water as well as require the further step of post treatment of the wash solution to remove contaminants from the wastewater. Unfortunately, aqueous washing can also prove ineffective for removing relatively hard contaminants, such as glass, sand, and the like, which may become embedded in the polyester materials.
In an attempt to remove embedded materials from polyester substrates, melt filtration processes have been used in which the contaminated polyester is melted and then filtered in order to remove the solid contaminants. These are not terribly cost effective methods, however, and often prove economically unfeasible.
What is needed in the art is a novel method for removing contaminants from polyester materials, and in particular, from post-consumer polyester materials. In addition, what is needed in the art is a polyester recycling process in which contamination levels of treatment water are reduced as compared to previously known recycling processes.